1. Field of the Invention
This invention relates to thermal management systems and, in particular, to a two-phase heat transfer system using heat pipe principles and to capillary-pumped equipment mounting panels employed therewith.
2. Description of the Prior Art
In current space activities, the very large, long-life space systems presently being planned are based on the large lift capabilities of the United States Space Shuttle. These large satellites and other space projects will require thermal management systems with multikilowatt capacity capable of collecting and transporting heat from various subsystems to heat rejection radiators. Transport distances are expected to be on the order of 10 to 30 meters. Current technology for large thermal transport systems is based on circulating liquid loops. These tend to be heavy and vulnerable to micrometeroid puncture, have relatively low thermal performance (film coefficients), and require significant amounts of pump power. As current demonstrated pump life is only 21/2 years, the pumps and the required valves also lower system reliability. Many problems inherent in thermal systems using a circulating liquid can be alleviated by using a capillary-pumped two-phase circulating system. Liquid delivered to the mounting panels on which heat generating equipment is fixed would pick up heat by evaporation. The vapor would be delivered to heat sinks, yielding heat by condensation. Compared to circulating liquid systems, mass flow rates and liquid line sizes would be reduced, film coefficients would be higher, and pump power would be eliminated.
Capillary pumped heat pipe systems are, of course, well known in the prior art both for ground-based and for space applications. In the prior art, also, J. T. Pogson et al. (U.S. Pat. No. 4,040,478) teach that it is known to provide heat pipe systems having separate evaporators and condensers connected for fluid communication therebetween by individual liquid and vapor lines. However, they do not provide a teaching of a system with an equipment mounting panel construction having a sheet wick in the panel interposed between the liquid grooves and the vapor channels therein such that a high capillary pressure for efficient fluid circulation in a heat pipe system is attainable.
There is a teaching by W. P. Peck (U.S. Pat. No. 3,803,688) of a heat pipe having an integral "screen wick" between the liquid capillary grooves and the vapor space of the device. Although the construction has a superficial resemblance to the panel design of the present invention, Peck provides capillary grooves for the required fluid circulation therealong and the screen wick disclosed therein does not act as a capillary pumping means as in the present invention but merely serves a vapor venting function. In addition, unlike Peck, the grooves of the present invention cover only a small fraction of the heat transfer surface, and the porous wicking which covers both the grooves and the remainder of the surface serves to draw liquid in a direction transverse to the groove axis to completely wet the surface. Evaporation occurs at the meniscus at the liquid-vapor interface near the exposed surface of the porous wicking.